The present invention relates to a process for starting up a reaction for the polymerization of an olefin in the gas phase in a fluidized bed in the presence of a catalyst of Ziegler-Natta type.
It has been observed that when the polymerization of an olefin is carried out in the gas phase in a fluidized bed, the formation of agglomerates and/or of polymer of an undesirable quality can often take place at the time of start-up of the polymerization. This appears in particular after having begun to introduce the catalyst into the fluidized bed and up to the time when a certain amount of polymer is produced, in particular up to the time when a stable level of full hourly production of polymer is achieved, that is to say the maximum level of hourly production desired.
It has also been observed that, during the start-up period, the instability of the polymerization conditions in a fluidized bed often leads to uncontrolled reactions and the formation of agglomerates.
A novel process for starting up a reaction for the polymerization of an olefin in the gas phase carried out in a fluidized-bed reactor has now been found which makes it possible to solve the problems mentioned previously. More particularly, the process of the invention makes it possible to initiate a polymerization reaction with a very limited, indeed zero, formation of agglomerates.